`JSON::ResumableParser` raises an error `unexpected end of input, expected closing " at line 1 column N`

[Watson1978]

First of all, thank you so much for your incredible work on the json gem and the recent addition of JSON::ResumableParser.
It is an amazing addition to the library.

when a string value is fed across a << boundary AND parse is called once while the parser is suspended in the middle of that string.
The value is then parsed correctly, but a later parse (which correctly returns false at end-of-stream) leaves a JSON::ParserError that surfaces at a later checkpoint.
The reported column points back to the opening quote of the string that straddled the boundary, which suggests stale frame state rather than a real parse condition.

Environment

• json: commit hash = 02346d8
• ruby: ruby 4.0.5 (2026-05-20 revision 64336ffd0e) +PRISM [x86_64-linux]

Reproduction

The trigger is a parse call between the two feeds, while suspended inside
the string:

require 'bundler/inline'
gemfile do
  source 'https://rubygems.org'
  gem 'json', git: 'https://github.com/ruby/json.git'
end

parser = JSON::ResumableParser.new({})
parser << '{"message": "hello '
p parser.parse      # => false  (needs more input; records mid-string frame state)
parser << 'world"}' # append -> buffer is reallocated, invalidating that state
p parser.parse      # => true
p parser.value      # => {"message"=>"hello world"}   (correct)
p parser.eos?       # => true   (buffer fully drained)
p parser.rest       # => ""     (no leftover bytes)
p parser.parse      # => false  ... but a deferred JSON::ParserError is raised

Result: all of the above print as commented, then:

... in 'JSON::ResumableParser#parse': unexpected end of input, expected closing " at line 1 column 13 (JSON::ParserError)

and the backtrace points at the intermediate parse call (the one that returned false).

The same path is hit by the natural streaming loop, where it raises during the loop.

require 'bundler/inline'
gemfile do
  source 'https://rubygems.org'
  gem 'json', git: 'https://github.com/ruby/json.git'
end

parser = JSON::ResumableParser.new({})
['{"message": "hello ', 'world"}'].each do |chunk|
  parser << chunk
  while parser.parse
    p parser.value
  end
end

Expected

The trailing parse should simply return false

Required preconditions

All three are needed; remove any one and it parses cleanly:

1. The << boundary lands inside a string that is a value within a container (object/array).
   A split between documents, or outside any string, is fine.
2. parse is called while the parser is suspended inside that string (it returns false).
   If both feeds happen before the first parse, there is no error.
3. More data is then fed (<<), appending to / reallocating the buffer String.

[Watson1978]

Additional: The error will be shown even if catch it with rescue

Even when using rescue to catch JSON::ParserError, the exception message will be displayed and the script will terminate with an error.

require 'bundler/inline'
gemfile do
  source 'https://rubygems.org'
  gem 'json', git: 'https://github.com/ruby/json.git'
end

parser = JSON::ResumableParser.new({})
['{"message": "hello ', 'world"}', '[1,2]'].each do |chunk|
  parser << chunk
  begin
    while parser.parse
      p parser.value
    end
  rescue JSON::ParserError
    parser.clear
  end
end

$ ruby resume3.rb
{"message" => "hello world"}
[1, 2]
resume3.rb:11:in 'JSON::ResumableParser#parse': unexpected end of input, expected closing " at line 1 column 13 (JSON::ParserError)
        from resume3.rb:11:in 'block in <main>'
        from resume3.rb:8:in 'Array#each'
        from resume3.rb:8:in '<main>'

$ echo $?
1

[byroot]

Thanks for the report, I will try to figure out what is going on. Very surprisingly, the reproduction script show the error when ran independently, but doesn't if I try to turn it into a unit test.

[Watson1978]

Thanks!